1,3-propanediol (PDO) can be prepared via hydrogenation of an aqueous solution of 3-hydroxypropanal. The 3-hydroxypropanal (HPA) intermediate solution can be prepared via a process involving the catalyzed hydroformylation (reaction with synthesis gas, H2/CO) of ethylene oxide to form a dilute mixture of HPA in an organic solvent, followed by extraction of the HPA into water to form a more concentrated HPA solution, and subsequent hydrogenation of the HPA to the PDO.
U.S. Pat. No. 5,786,524, which is incorporated herein by reference, describes such a process wherein ethylene oxide and synthesis gas are contacted at 50 to 100° C. and 500 to 5000 psig in the presence of a cobalt or rhodium catalyst and a catalyst promoter to produce an intermediate product mixture comprising HPA. Water is added to the HPA mixture and most of the HPA is extracted into the water to provide an aqueous phase comprising a higher concentration of HPA and an organic phase containing at least a portion of the catalyst. The aqueous phase is separated from the organic phase and then diluted with an aqueous solution of 1,3-propanediol. This aqueous solution is then passed into a hydrogenation zone in contact with a fixed bed hydrogenation catalyst to form an aqueous solution comprising PDO and then the PDO is recovered.
Alternately, hydration of acrolein, as described in U.S. Pat. No. 5,015,789 which is herein incorporated by reference, may be employed to produce the aqueous intermediate stream of 3-hydroxypropanal.
U.S. Pat. No. 5,945,570, which is herein incorporated by reference, describes a novel hydrogenation catalyst for use in the hydrogenation of 3-hydroxypropanal. The catalyst is a promoted nickel catalyst which also comprises molybdenum and a binder material which can be a silicate or an oxide of silicone, zirconium, aluminum, etc. The catalyst system is characterized by a prolonged catalyst life in the hydrogenation reaction environment because of the increased crush strength of the catalyst system with respect to prior catalyst systems such as the supported hydrogenation catalyst system described in U.S. Pat. No. 5,786,524 discussed above.
During the hydrogenation process or in steps preceding the hydrogenation process, significant concentrations of HPA and PDO may coexist. These components may react to form the thermodynamically favored cyclic acetal MW132:
Further reaction of the cyclic acetal may occur, to produce additional byproduct species.
It would be highly advantageous if the reverse reaction, i.e., the reaction of the acetal to PDO could be encouraged during hydrogenation, as this would increase the yield of PDO. However, the extended life catalyst described in U.S. Pat. No. 5,945,570 does not actively promote the reversion of acetal back to PDO and HPA (where the latter would then be hydrogenated to PDO). The current invention allows efficient reversion of acetal byproducts to PDO at improved space-time yields.